Angular adjustment devices are often used in internal combustion engines in order to shift the position of the camshaft relative to the crankshaft by a predetermined angle. The camshafts operate the valves according to the profile of their cams, the resulting fixed valve control times merely representing a compromise, above all with respect to the rated power, torque, fuel consumption and exhaust gas emission requirements of the internal combustion engine. The phase shift of the control times associated with the adjustment in the angular adjustment serves the purpose of optimisation.
The angular adjustment is mostly effected hydraulically, and a fall in the hydraulic pressure below a lower limiting value may lead to undesired positions of the camshaft relative to the crankshaft, which are accompanied by high loads on the components. In order to avoid undesired positions of the camshaft in case of inadequate hydraulic supply it is known to provide a device which, if the hydraulic pressure is too low, brings the camshaft into a base position and arrests it in this position until the oil pressure has reached an adequate value for stable control of the system, for example after starting the internal combustion engine. Otherwise, it can in fact happen that until the predetermined oil pressure has been reached an uncontrolled angular adjustment occurs which in case of a possibly necessary repetition of the starting of the internal combustion engine leads to starting problems.
German Offenlegungsschrift 39 37 644 discloses a device for hydraulic angular adjustment in which an impeller wheel attached coaxially on the shaft side is received in a cellular wheel secured on the driving wheel side. A device for arresting the shaft in its base position includes a slidably movable arresting sleeve located coaxially in the cellular wheel or impeller wheel and held non-rotatably by means of a locking profile, and blocking grooves located in the respective counterpart wheel and aligned with the locking profile, the arresting sleeve being moved out of the arresting position by a servomotor. A disadvantage of this device is that it requires a relatively large amount of space in the axial direction of the shaft and is expensive to make both mechanically and in respect of control technology.